a graded exercise test protocol (treadmill, cycle ergometer, arm ergometer, or step) by the indirect calorimetry method with a sophisticated stationary metabolic cart or a telemetry metabolic system.1,32 A healthy person’s maximal physical capacity is related to age, gender, and training status. With aging, there is approximately a 1%
reduction in VO2 max per year between 25 and 75 years.33 In general, for an individual to carry out a full-time job, the physical demand for that job should not exceed 40%
of their maximal physical capacity.34
Many factors affect the energy expenditure of physical activities in healthy people. Intrinsic factors affecting energy consumption, defi ned as factors that come from the body itself, include the following: gender, age,9,13,23 body composition,3 fi t-ness level (trained versus sedentary),13 muscle fi ber type (oxidative versus glycolytic metabolism), degree of muscle atrophy, muscle strength, range of motion, and hemoglobin content (anemia, polycythemia).1 With aging, there is a decline in the economy of walking.8,13,35 Males have a better fi tness level than females due to a greater proportion of lean body mass and hemoglobin content,1 yet both genders are shown to have similar economy of walking.35 Adolescents have a relative high energy expenditure of walking and a low gait effi ciency when compared to adults.6 Obese people were shown to have a similar gait effi ciency as people with normal weight.3
Extrinsic factors affecting energy consumption of activities, defi ned as factors coming from the environment or devices, include the following: mode of exercise (treadmill versus over ground walking),36,37 speed and grade of treadmill,5,8,24 fl oor surface, footwear, the amount and the location of loading,38 type of device used (e.g., crutch, cane, and walker), patterns of gait (swing through, reciprocal), orthotic use, weight-bearing status, posture, and wheelchair use. Walking on treadmill allows for convenient measurement of physiologic parameters, has a low intercycle variability of gait, and is commonly used for multiple-speed gait studies. Energy expenditure during treadmill walking was shown to underestimate the energy expenditure of fl oor walking,36,37 but studies on the difference of energy consumption between fl oor walking and treadmill walking have been equivocal.7,36,39,40
Walking movements are robust against changing loads based on a computer simulation study.41 Based on the magnitude and the location of the added mass, the movement of the system will convert to a new steady state as described by a limit cycle, which is structurally stable against changes in inertial conditions within a cer-tain range. Specifi cally, the upper limits of the mass affi xed to the parts of the body are 5, 15, 5, 1, and 0.5 kg of the HAT (head, arms, and trunk), pelvis, thigh, shank, and foot, respectively. This might also explain the negligible effects on energy expen-diture in some studies when large loads were applied to the center of gravity of the body,42 or when a small weight was applied to the ankles.43 This is in contrast to reports that showed a signifi cant effect of a large load on the energy expenditure of walking when placed on distal foot segments.38,44
2.2 ENERGY EXPENDITURE IN PEOPLE WITH
2.2.1 AMPUTATION
Major lower extremity amputation often is associated with signifi cant mortality and morbidity rate, especially for vascular amputation.45 Prosthesis fi tting and ambu-lation mark an important milestone for an amputee. With advances in prosthe-sis design and technology, problems of increased energy expenditure of walking and a slow comfortable walking speed associated with prosthesis have greatly improved.17,18,25,46–51
Factors affecting the increased metabolic demand of walking in amputees could again be either intrinsic or extrinsic. The intrinsic factors are related to the level of amputation,18 length of the residual limb,52 cause of amputation, gait asym-metry, muscle atrophy in the amputated limb, and physical fi tness of the amputee.53 The extrinsic factors are related to devices of walking, type of prosthesis foot,54,55 weight of prosthesis,56 prosthesis components,57,58 and crutches versus prosthesis use. From a biomechanical perspective, the increased metabolic cost of gait was shown to be related to the increased mechanical work, the disturbance of the sinu-soidal changes of the center of body mass and the effi ciency of the pendulum-like mechanism.59
In general, lower limb amputees who have a higher level of limb amputation will have a higher energy expenditure of walking. The order of energy expenditure for different levels of amputation is generally as follows: transfemoral (above knee) amputation > transtibial (below knee) amputation > Syme (ankle) amputation.18,60 However, a longitudinal case study showed that the energy expenditure of walking for an amputee using a below-knee prosthesis was not worse than that with a Syme prosthesis, because a dynamic response foot of a below-knee prosthesis enhanced the energy restore at the ankle.61
With well-fi t prosthesis, muscle strengthening, and gait retraining, a skilled pros-thesis user can save the energy of walking much more than walking with crutches,18,62 but walking with a prosthesis may not provide a better functional outcome if the expense of energy is too high. For example, the use of crutches was shown to provide a faster walking speed and a less amount of energy expenditure in vascular unilateral transfemoral patients.18 Wheeling was shown to be more practical, having a faster speed of transportation and a lower amount of energy expenditure than walking with a prosthesis or crutches for a bilateral transfemoral amputee.63
At the same level of lower limb amputation, traumatic amputees generally have a better economy of gait and require less energy expenditure of walking than that of vascular amputees. This is because the traumatic amputees are generally younger, have a higher fi tness level, and fewer cardiovascular comorbidities.64–66 The success rate for prosthesis fi tting and rehabilitation in general is better in traumatic amputees than in vascular amputees.
In recent years, there has been much research on the optimal inertial properties of prosthesis that would improve energy effi ciency and gait symmetry. Effects of heavyweight prosthesis on the energy expenditure of walking and gait largely depend on the inertial properties of the prosthesis leg and the type of amputa-tion.56,67–70 Small amounts of added prosthetic mass67 or even matching up to the intact limb mass, without shifting the center of mass of the leg, did not increase
energy expenditure of walking in below-knee amputees.56 However, distal loading to the prosthesis,71 or matching the prosthesis’ moment of inertia to the intact leg, had detrimental effects on gait parameters and the energy expenditure.68 Furthermore, amputees were shown to adopt similar kinematic patterns and adjust joint torques in response to the small prosthetic mass perturbations.69 Currently, lightweight pros-thesis is no longer the trend of prospros-thesis manufacturing for traumatic amputees.
Some advanced suspension systems, such as the suction type of suspension and the suspension sleeve, are designed in a way to tightly hold the heavy prosthesis to the stump or residual limb. It is likely that the optimal inertial properties of a prosthesis leg for amputees could be found in the near future. However, people with vascular amputation often have other comorbidities and poor physical capacity, so they prob-ably could not take advantage of heavy prosthesis without the increased burden of energy expenditure.
Many studies in the literature have documented the effects of prosthesis foot type on the energy expenditure and the biomechanics of gait.54,55,64,65,72–75 It has been shown that different types of dynamic response foot design incorporated fl ex-ibility and force-producing capability in the foot or shank of the prosthesis, which leads to reduced energy expenditure and improved gait effi ciency when compared to traditional solid ankle cushion heel (SACH) foot. The dynamic response foot is especially benefi cial during faster walking speeds or running.55 However, it appears that no specifi c type of dynamic response foot is superior, and this awaits further research.
Walking has been modeled as an inverted pendulum, i.e., energy is exchanged between kinetic energy and gravitational potential energy from one stride to the next stride.76 However, the human pendulum is not an ideal frictionless pendulum system, so the maximum exchange is only about 65%.77 For amputee gait, the energy exchange is generally not as good as that of normal subjects. With rehabilitation, amputees showed a better energy exchange, a higher SSWV, and a better gait effi -ciency.59 This is similar to the observation that women of East Africa are able to carry heavy head-supported weight, because they have an improved energy trans-fer from step to step through many years of practice.78 By adding prosthetic mass in transfemoral amputees, they were also shown to have a better energy exchange between steps (effectively conserving the mechanical work), no increase in meta-bolic cost of walking, and a faster comfortable walking speed.79 Table 2.3 shows the energy expenditure and gait effi ciency at comfortable speed in amputees.
2.2.2 JOINT IMMOBILIZATION
Immobilization of different lower limb joints was shown to result in increased energy expenditure, reduced walking speed, and reduced economy of walking due to the altered biomechanics of lower limb segments.17 Among the different joints, ankle immobilization has the least effect on energy expenditure (about a 6% increase), when compared to knee or hip immobilization. The effect of knee immobilization on energy expenditure depends on the knee angle, with a knee angle of 165°, resulting in the lowest (10%) increase in energy expenditure, and a knee angle of 180°, resulting in a 13% increase in energy expenditure.17
TABLE 2.3
Energy Expenditure and Gait Effi ciency at Comfortable Speed in Amputees
References Subjects Speed (m/min)
Oxygen Consumption
(mL/kg/min)
Gait Effi ciency (Net O2 Cost)
(mL/kg/m) Waters et al.18 Prosthesis use
Vascular amputees
Above knee 36 ± 15 12.6 ± 2.9 0.35 ± 0.06
Below knee 45 ± 9 11.7 ± 1.6 0.26 ± 0.05
Syme 54 ± 10 11.5 ± 1.5 0.21 ± 0.06
Traumatic amputees
Above knee 52 ± 14 12.9 ± 3.4 0.25 ± 0.05
Below knee 71 ± 10 15.5 ± 2.9 0.20 ± 0.05
Crutches use Vascular amputees
Above knee 48 ± 11 15.0 ± 2.9
Below knee 39 ± 13 14.6 ± 1.5
Syme 39 ± 14 12.8 ± 4.3
Traumatic amputees
Above knee 65 ± 16 15.9 ± 5.4
Below knee 71 ± 10 22.4 ± 4.3
Pagliarulo et al.47
Traumatic below knee
71 15.5
Gailey et al.67 Traumatic below knee
76 12.8
Normal subjects 76 11.2
Lin-Chan et al.61
Traumatic below knee (single case)
79–80 — —
Hsu et al.54 Traumatic below knee
71 — —
2.3 ENERGY EXPENDITURE IN PEOPLE WITH